A hot water supply system includes a heat source unit such as a heat pump or a boiler and a hot water storage tank that stores hot water, and is able to store hot water in the hot water storage tank by using the heat of a heat medium heated by the heat source unit. The hot water stored in the hot water storage tank is used for the application of hot water supply for a shower or a bath, a kitchen, or the like.
A method for generating hot water to be stored in the hot water storage tank includes a direct heating method in which hot water heated by the heat source unit is stored directly in the hot water storage tank; and an indirect heating method in which heat is exchanged between a refrigerant or a heat medium heated by the heat source unit and hot water in the hot water storage tank.
As a hot water supply system employing the direct heating method, there is a hot water supply system that includes a heat pump having high energy efficiency as a heat source unit, and a large-capacity hot water storage tank, and boils a large amount of hot water at late night at which the electricity unit price is low.
In addition, as a hot water supply system employing the indirect heating method, a system has been proposed which includes a water heat exchanger that exchanges heat between a refrigerant flowing through a primary side circuit and water flowing through a secondary side circuit and in which heating energy of the refrigerant heated by a heat source unit is transmitted via the water heat exchanger to the water flowing through the secondary side circuit, thereby generating hot water (see, e.g., Patent Literature 1).
In the technique described in Patent Literature 1, when an amount of heat in a hot water storage tank is insufficient, reheating of water is performed to increase the amount of heat. Prior to the reheating, a hot water supply load for the current day is predicted on the basis of a load result for past 7 days, and, at the day of control, when the load result becomes greater than a predicted load for four hours later, reheating is performed with the difference between the load result and a predicted load at the current time as an additional amount of heat to be stored. By so doing, when the time slot when a hot water supply load is generated is a time slot before a time slot in which the prediction is made, it is possible to make an amount of reheating appropriate. Thus, it is possible to suppress an unnecessary reheating operation to improve the energy saving property of the hot water supply system.